A new technique is proposed for the preparation of pure aluminium mirror surfaces for ultraviolet astronomical instruments in orbiting space vehicles. Pure aluminium surfaces can provide high reflectivity at ultraviolet wavelengths in the region 90-120 nm which is not effectively provided by conventional Al+MgF₂ mirror surfaces. The proposed 'REVAP' technique uses a removable volatile protective coating to cover the pure aluminium surface during the time interval between the initial evaporation in the laboratory and the subsequent 'revaporisation' in the space environment.